The invention relates to fastener installation apparatus, and more particularlY to apparatus for installing fasteners of the type comprising a first member, a second member, and a third member, the fastener being installed bY the application of force to the second member relative to the first member, the reaction to the force on the second member being applied to the first member through the third member, the third member being free from the first and the second members on completion of the installation of the fastener
The fastener installation apparatus will comprise a first part for engaging the third member to transmit reaction force therebY to the first member, and a second part for engaging the second member to apply force thereto relative to the first member.
More specificallY, the fastener may be of the tYpe in which the first member comprises a tubular shell, the second member comprises a stem inserted into the tubular shell, force being applied to the stem with respect to the shell in order to install the fastener, the reaction to the force on the stem being applied to the shell through the third member which comprises an annular member in contact with the shell and through which the stem also passes.
The installation apparatus for installing such a fastener will normally comprise a first part in the form of an annular face for contacting the annular third member and surrounding an aperture into which the fastener stem is inserted, and a second part comprising stem-engaging means for engaging the stem when the latter is inserted into the aperture.
The third member of the fastener, which is part of the fastener assembly before installation but is free of the installed fastener on completion of installation, acts as a temporary engagement interface between the first part of the installation apparatus and the first member of the fastener. This removes the need for the first part of the apparatus to engage directly with the first member of the fastener.
One example of such a fastener is that marketed under the trademark CHERRY-MAX, and described in British Patent specification No. 1 490 508. In this fastener pulling force is applied to the stem with respect to the shell to cause the stem to move longitudinally with respect to the shell to install the fastener. The annular third member takes the form of a washer assembled on the stem and in contact with the end of the shell. The thrust, which is the reaction to the pull on the stem, is applied by the annular face of the installation apparatus to the end of the shell through the washer, which is also in contact with the annular face of the installation apparatus. On the completion of installation, the stem breaks off level with the end of the shell and the washer is free of the installed fastener.
Another example of such a fastener is a development of the previous example, in which the washer is provided with an annular rim projecting towards the associated shell. On installation of the fastener, the reaction force between the annular rim and the shell deforms the shell so as to form a lock between the shell and the stem. This type of washer is referred to as a lock creator, and fasteners embodying it are known under the trademark LOCK CREATOR MBC or MBC LC.
A further example of such a fastener is that marketed under the trademark COMPOSILOK-II, and described in European Pat. Publication No. 0 152 531. In this fastener the stem and shell are in threaded engagement with each other, and force is applied to the stem with respect to the shell to cause the stem to rotate with respect to the shell, to install the fastener. The annular third member takes the form of a drive nut also threaded on the stem and in contact with the end of the shell. The torque reaction to the rotational force applied to the stem is transmitted by the friction between the drive nut and the shell. On the completion of installation, the drive nut is free of the installed fastener, in threaded engagement with a broken-off portion of the stem.
Fasteners incorporating such intermediate third members are advantageous in that the third member can be shaped and/or dimensioned on one side to engage appropriately with the associated first member of the fastener, at the same time as having the other side of shape and/or dimensions appropriate to engage with standardized first part of the installation apparatus. It is easier and cheaper to manufacture a range of fasteners with third members of different designs, than it is to manufacture a range of fastener installation apparatus with different designs of the first part thereof. This enables the same fastener installation apparatus to install fasteners of different sizes or types of first member. In addition, the presence of the third member during the installation process may, in some circumstances, protect the shell of the fastener and/or the surrounding workpiece in which it is installed from accidental damage by the first part of the installation apparatus.
The disposable lock creator, which is provided as part of each fastener assembly, has to function only once and is then thrown away, and is relatively cheap to manufacture. It replaces a previous similar annular rim which was an integral part of the installation tool annular face, which is expected to function many tens of thousands of times, and is therefore more difficult and expensive to manufacture and to replace, but is subject to wear and vulnerable to damage.
However, the use of fasteners incorporating such intermediate third members has a disadvantage. Since at the completion of .the installation of each fastener the third member is free from the installed fastener, the third member, such as the washer, or lock creator, or drive nut (with a piece of broken-off stem still in threaded engagement with it), then falls away from the installed fastener. It thus causes contamination of the surroundings of the installed fastener. It may fall on a factory workbench or a workshop floor, or it may fall down inside the body of an automobile, aeroplane or aerospace vehicle in which the fastener has just been installed. This may be a hazard, and in many applications this may be so dangerous that the use of such fasteners is not possible.